The traditional entrepreneurial spirit of the United States was driven by the culture of immigrants. Over 40% of the companies on the Fortune 500 were founded by immigrants or the children of immigrants. These were once disruptive startups.
Now we make it very difficult for talented and intelligent people to become permanent residents. So instead they stay home, or maybe go to Canada or Australia.
It's true that immigration was freer prior to the 1930s, but today is better than any other time post-WW2, in terms of the % of the population that is foreign-born, the # of naturalized citizens, the # of permanent residencies granted, etc.
It's funny while America is hated, and some other countries are touted to have better systems and will soon take over America's leadership, tons of people are voting for America with their feet, and crying for green cards.
http://web.mit.edu/cis/images/fpi/immigration/fig1.jpg
http://web.mit.edu/cis/images/fpi/immigration/fig3.jpg
If correlations prove anything (note: I don't think they prove much), it is that immigrants inhibit startup formation.
How difficult can it really be to stay?